I can't answer your question but I'm suprised RCS hasn't straightened us out yet. I took some pics of some of my gas cylinders for comparison. The only problem being I can't tell you if the gas cylinder on my IHC is IHC or not, but I think it is.
This is the IHC, it seems to have more rounded corners.

This is a mid 1941 LL Springfield

This is a 5.9 million Springfield

This is an H&R


The machining here is a little different on each brand.
IHC

Early SA

Late SA

H&R


The flat on the top of the back ring is different sizes(not saying they didn't machine the parts differently at different times at the same factory, I don't know).
IHC is a lot wider, approx. .380"

Early SA, approx. .280"

Late SA, approx. .280"

H&R, approx. .250"


All of this means absolutly nothing because none of it can be verified but at least it gives us something to look at.
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.